1. Field of the Invention
The invention relates to an extending prop for underground mining or tunnel construction, consisting of two telescopic tubes which are closed at their free ends and designed to be braced against the rock by means of a hydraulically operating prop-extending device, with provision being made between said tubes for a locking device, by which the inner tube can be mechanically fixed on the outer tube at different lengths of extension, whereby the interior spaces of the extending prop can be filled with construction material while the extension load is being maintained.
2. The Prior Art
Such extending props filled with construction material are now frequently used instead of the wooden props or individual hydraulic props employed in the past. The advantage is that such props, given their lightweight construction, are capable of generating very high forces of support. Since the tubes substantially only serve as tension-resistant sleeves for the largely compression-resistant construction material, their steel construction can be designed with consequent application of the design principles of lightweight engineering. Simple welded tubes made of inexpensive structural steel can be used because stressing of the tubes is not critical. The weight of the props is very light as long as the tubes are still empty, so that they can be easily transported and handled at the site of installation. Because of the lightweight design and inexpensive manufacture made possible by such a design, said props, as opposed to individual hydraulic props, can be used as so-called "lost expansion" which, after it has been used, for example in the brace/gallery transition zone, can be left standing without problems in the packing space. Such lost expansion within the zone of the edge of the gallery, furthermore, offers advantages in view of the future stability of the gallery.
Such a prop filled with construction material is known, for example from DE-PS 41 15 209. Before the construction material is filled, said known prop uses for bracing a plurality of hydraulic clamping cylinders, which are attached to the outer and inner tubes from the outside for displacing the inner tube against the outer tube. In the extended position, the inner tube is locked on the outer tube in the given position of extension by a locking device. The hydraulic clamping cylinders then can be removed. Subsequently, the prop so braced against the rock is filled with construction material.
The known prop of said type has drawbacks in various respects. On the one hand, handling of the hydraulic clamping cylinders is extremely complicated and labor-intensive. Each of said heavy clamping cylinders has to be lifted by hand, attached to the prop, and then removed again from the latter after bracing has been completed. On the other hand, possibilities have to be available for connecting the cylinders with a high-pressure hydraulic system, for example a connection with the bracing hydraulics. Furthermore, the flow of forces obtained is unfavorable because of the lateral attachment of the clamping cylinders. In addition, the extent of telescoping is relatively limited.
Finally, another drawback is that the prop can absorb only low forces until it is filled with construction material, because the mechanical locking device always first requires a certain amount of insertion of the inner tube against the outer tube before it is capable of absorbing notable forces. The known props, therefore, are not sufficiently bearing in the early stage and require a relatively large amount of convergence before developing their full supporting force.
The older DE 43 38 830 Cl--which was not published at an earlier date--discloses a similar extending prop, in which the inner end of the inner tube is designed closed, forming in this way a piston that is guided sealed in the outer tube. The interior space of the extending prop is divided by such cylinder in two chambers, which both can be filled with construction material, for example with compressible foamed concrete. With said extending prop, however, the piston does not serve the purpose of setting the prop with high setting load, but for obtaining in cooperation with the compressible filling material a defined yieldingness of the prop. For extension, said known prop uses a prop extension mechanics, which is located at the insertion end of the outer tube and fixable on the inner tube with vertical adjustability. No high extension loads can be achieved with said mechanical prop extension device. Furthermore, it is not possible to achieve high extension loads by filling the interior spaces of the prop with expanding foam material because the latter is compressible and, consequently, not capable of generating any high extension load.
An extending prop is known also from WO 94/27029, which consists of two telescopic tubes which are closed at the ends facing away from each other. The tubes can be hydraulically braced against the rock and fixed on each other with a locking device at different lengths of extension. The outer tube and the inner tube enclose a chamber, which can be acted upon via a filling connection by pressure medium, whereby the inner tube is extended from the outer tube, i.e., the extending prop is set. However, the interior spaces of this known prop cannot be filled with construction material, which means that the advantages of this special technology are not exploited.
The problem of the invention is to create an extending prop of the type specified above, which can be handled in a simple way, extended hydraulically with high extension load; which has immediate or at least early bearing characteristics, and which can be filled with construction material over its entire length.